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In order to understand the importance of soft jaws in the manufacturing industry, we first need to get an understanding of standard work holding methods for CNC machines.

There are two ways to hold down a part that will be machined; the first being a lathe, which in most cases means that a three chuck grasp holds the part precisely and concentrically for it to be worked on. The second method is to use a milling vise that is bolted onto a milling table and can hold parts securely while an end mill or some other machining tool performs operations.

These two methods are standard for a majority of manufacturing processes; however, they do not cover the entire spectrum of requirements for CNC machining. This is where soft jaws come into play.

Equipping a lathe with soft jaws will allow complex shaped parts to be grasped securely and concentrically. Another option is to create a non-marring aluminum fixture so that they can hold a large steel part to be machined.

Soft jaws can also be used on a mill to hold down parts that are too small or irregularly shaped and provide a tight grip so that they can be machined properly.

Given the importance of soft jaws in the CNC machining process, what would determine the use of 3D printing to produce them?

We can start off by conducting a quick analysis of the time and cost (interrelated) it takes to manufacture soft jaws using traditional methods.

While soft jaws are incredibly useful in the manufacturing process, they can pose quite a few issues with respect to the way they are produced. Soft jaws are not end use parts, which means that they do not have any implicit value and do not contribute to the bottom line. Using a CNC machine to produce soft jaws generates a cost to the business that is represented by machine downtime and the added labor costs associated with human supervision of the process. 3D printing eliminates this cost as the entire manufacturing process is hands-off and does not generate any CNC machine downtime. The 3D printer will build the part without human supervision while your workforce and CNC machine can continue to produce parts that contribute to overall profitability.

Another way to assess costs associated with the production of soft jaws is by taking into consideration the impact on the total cost of end use parts. For small run end use parts produced with the help of a soft jaw, manufacturing soft jaws by CNC might turn out to be prohibitively expensive because it can add up to 2x the cost of the actual end use part. With the 3D printing method there is no implicit machine downtime cost. The cost for a 3D printed soft jaw consists of only the cost of the materials required, whereas the cost of a machined soft jaw is made up of both materials and the implicit cost generated by machine downtime.

Now let’s take a quick look at some of the factors that need to be considered when 3D printing soft jaws.

There are three critical properties to take into account:

1. Part stiffness

Soft jaws need to withstand a significant clamping force without bending, or breaking; otherwise you risk sacrificing the part itself or its accuracy. While most 3D printing methods use thermoplastics alone and cannot guarantee a satisfactory level of stiffness, Markforged utilizes a unique combination of composite reinforcements with continuous fiber glass delivering parts that are stiff and strong enough to withstand machine forces.

2. Chemical resistance

Most 3D printing plastics are not chemically resistant due to their composition and fabrication method. The risk here is that cutting fluids tend to dissolve these fixtures, which means that as the machine process goes on, the fixture becomes less and less effective until it is no longer functional at all.
Markforged has a solution to this problem – Nylon based thermoplastics. These unique materials are able to stand up to harsh chemicals including cutting fluids which means they can be utilized in the most intense CNC machine (as long as the soft jaw itself is not milled).

3. Non-marring properties

Soft jaws must be non-marring in order to produce parts with excellent surface finish quality, and robust enough to withstand the machining process.